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We test the effects of seed mass, temperature (16 degrees C, 24 degrees C, 30 degrees C), and seed age (1 year, 7 years, 20 years) on the germination rates of two and zone plant species that differ in seed mass, but occur within the same genus (Frankenia) to determine whether these factors, or a combination of these factors, influence germination rates. Frankenia serpyllifolia sens. lat. produces one or two larger seeds per fruit whereas F.foliosa produces up to 27 smaller seeds per fruit. Both of these species co-occur geographically in northern South Australia and experience similar abiotic conditions (unpredictable rainfall, extremes in temperature, poor soil conditions). The results showed that germination success by Day 21 was similar between the species, whereas we found significant differences in germination rates during the first week. Frankenia serpyllifolia sens. lat. seeds germinated rapidly and were less temperature dependant for germination success. Frankenia foliosa seeds were relatively slower to germinate and germination rates were higher at lower temperatures. Differences in germination rates were demonstrated to result from an interaction between seed mass/seed age (eta(2)(P) = 0.30), and an between seed age/temperature (eta(2)(P)-0.19). but only minimally front an interaction between seed mass/seed age/temperature (eta(2)(P) = 0.08)